Multi-species ion acceleration from sub-ps, PW interactions with ultra-thin foils

Multi-species ion acceleration from ultra-thin foils was studied experimentally, employing the Vulcan Petawatt laser at the Central Laser Facility, UK. Plastic (CH) foils with thicknesses in the range 10–340 nm were irradiated with intense, short (750 fs) laser pulses producing maximum energies of ∼65 MeV and 25 MeV/nucleon obtained for H+ and C6+ ions, respectively. Ion spectra obtained from high resolution spectrometers suggest differences in the acceleration dynamics for the two species. Comparisons are made with two-dimensional Particle in Cell simulations, which identify, for an optimal thickness, two main mechanisms contributing to the ion acceleration process, namely multi-species target normal sheath acceleration (TNSA) and radiation pressure acceleration (RPA). Ion energies are further enhanced by the onset of relativistically induced transparency. A final stage in the acceleration is caused by the formation of electron jets (as the target undergoes transparency), which accelerate the ions off-axis. By analysing the spatial and temporal evolution of the accelerating fields, we are able to infer the effect of the different mechanisms on each species and how this translates to the experimental observations. The two main mechanisms, TNSA and RPA, are seen to each produce a distinct population of high energy protons whereas a single population of carbon is accelerated by a summation of these effects. This species-specific analysis sheds new light on the complex dynamics in a multi-species target expansion and on the contribution of different acceleration processes to the acceleration of the most energetic ions in the spectrum

Drone-based large-scale particle image velocimetry applied to tidal stream energy resource assessment

Resource quantification is vital in developing a tidal stream energy site but challenging in high energy areas. Drone-based large-scale particle image velocimetry (LSPIV) may provide a novel, low cost, low risk approach that improves spatial coverage compared to ADCP methods. For the first time, this study quantifies performance of the technique for tidal stream resource assessment, using three sites. Videos of the sea surface were captured while concurrent validation data were obtained (ADCP and surface drifters). Currents were estimated from the videos using LSPIV software. Variation in accuracy was attributed to wind, site geometry and current velocity. Root mean square errors (RMSEs) against drifters were 0.44 m s−1 for high winds (31 km/h) compared to 0.22 m s−1 for low winds (10 km/h). Better correlation was found for the more constrained site (r2 increased by 4%); differences between flood and ebb indicate the importance of upstream bathymetry in generating trackable surface features. Accuracy is better for higher velocities. A power law current profile approximation enables translation of surface current to currents at depth with satisfactory performance (RMSE = 0.32 m s−1 under low winds). Overall, drone video derived surface velocities are suitably accurate for “first-order” tidal resource assessments under favourable environmental conditions

Under- treatment and under diagnosis of hypertension: a serious problem in the United Arab Emirates

BACKGROUND: Hypertension, notably untreated or uncontrolled, is a major risk factor for cardiovascular diseases (CVD) morbidity and mortality. In countries in transition, little is known about the epidemiology of hypertension, and its biochemical correlates. This study was carried out in Al Ain, United Arab Emirates, to characterize self-reported (SR) normotensives and hypertensives in terms of actual hypertension status, demographic variables, CVD risk factors, treatment, and sequalae. METHODS: A sample, stratified by SR hypertensive status, of 349 SR hypertensives (Mean age ± SD; 50.8 ± 9.2 yrs; Male: 226) and 640 SR normotensives (42.9 ± 9.3 yrs, Male: 444) among nationals and expatriates was used. Hypertensives and normotensive subjects were recruited from various outpatient clinics and government organizations in Al-Ain city, United Arab Emirates (UAE) respectively. Anthropometric and demographic variables were measured by conventional methods. RESULTS: Both under-diagnosis of hypertension (33%) and under-treatment (76%) were common. Characteristics of undiagnosed hypertensives were intermediate between normotensives and SR hypertensives. Under-diagnosis of hypertension was more common among foreigners than among nationals. Risk factors for CVD were more prevalent among SR hypertensives. Obesity, lack of exercise and smoking were found as major risk factors for CVD among hypertensives in this population. CONCLUSION: Hypertension, even severe, is commonly under-diagnosed and under-treated in the UAE. Preventive strategies, better diagnosis and proper treatment compliance should be emphasized to reduce incidence of CVD in this population

Absolute calibration of Fujifilm BAS-TR image plate response to laser driven protons up to 40 MeV

Image plates (IPs) are a popular detector in the field of laser driven ion acceleration, owing to their high dynamic range and reusability. An absolute calibration of these detectors to laser-driven protons in the routinely produced tens of MeV energy range is, therefore, essential. In this paper, the response of Fujifilm BAS-TR IPs to 1–40 MeV protons is calibrated by employing the detectors in high resolution Thomson parabola spectrometers in conjunction with a CR-39 nuclear track detector to determine absolute proton numbers. While CR-39 was placed in front of the image plate for lower energy protons, it was placed behind the image plate for energies above 10 MeV using suitable metal filters sandwiched between the image plate and CR-39 to select specific energies. The measured response agrees well with previously reported calibrations as well as standard models of IP response, providing, for the first time, an absolute calibration over a large range of proton energies of relevance to current experiments

Atypical interaction: Conversation analysis and communicative impairments

In this article I review conversation analytic work on “atypical interaction”—social interactions where a participant has a communicative impairment. Drawing together some of the main themes and findings in the field, I highlight three forms of atypicality in these interactions, with each linked to more than one type of communicative impairment: (a) atypical forms of delay in TCU progressivity; (b) atypical problems of understandability, intelligibility, and hearing; and (c) atypical actions. I also discuss forms of atypicality that appear to arise from one or more participants adapting their talk or conduct to deal with the impact of the impairment within interaction. The article concludes with some considerations of directions that future work in this field might take. Data are in British and Australian English